1. Field of the Invention (Technical Field)
The present invention relates to the field of impulse radiating antennas, specifically to wideband collapsible and portable impulse radiating antennas for ease of transport and deployment in the field.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
The present invention is a collapsible impulse radiating antenna (xe2x80x9cCIRAxe2x80x9d), which is a compact and lightweight implementation of the general class of antennas known as impulse radiating antennas (IRAs). IRAs are well suited for radiating an extremely broad band of signal frequencies at reasonable gain throughout the band. While the antenna gain is not optimal at any one frequency, it is sufficient for many applications over frequency ranges of around two decades (100:1 frequency ratio). Such devices also provide the ability to radiate an impulse-like electric field, when driven by a step-like voltage. Furthermore such devices are typically well matched to a 50-ohm impedance, so there is little power lost due to reflection from the antenna back into the source. Reflector IRAs generally consist of a parabolic reflector with a transverse electromagnetic (TEM) feed resulting in very broadband performance (2 decades) with a very narrow beam.
IRAs are useful in a wide variety of applications, including broadband communications and broadband radar. Broadband communications may include two distinct types of communication. First, broadband communications include conventional narrowband communications that are swept in frequency over large bandwidths. As an example, one may wish to listen to a very broad range of frequencies (or radio channels) without changing antennas. Second, broadband communications may include the radiation or reception of instantaneously broadband signals, which are often impulse-like in shape. This mode of communication is primarily digital, and is commonly implemented with pulse position modulation. In this form of modulation, a one or a zero is interpreted based on the time of arrival of an impulse relative to some time standard.
Broadband radar, like broadband communications, can encompass methods that require the use of either narrowband signals that are swept over a broad frequency band, or the use of signals that are instantaneously broadband or impulse-like. Broadband radar can have applications in the detection of mines or unexploded ordnance. It can also have application in the detection of cracks in road beds or in bridges. Furthermore, it can have applications in target identification, where the broad bandwidth is utilized to provide more information than what is normally generated by a narrowband radar system. Finally, broadband radar can be useful in Synthetic Aperture Radar (SAR), which can be used to map out ground features from the air.
An IRA enables a single antenna to perform multiple narrowband missions on a platform, such as a ship or satellite, with limited space available for antennas. While each of the missions may be intrinsically narrowband, the combined mission of the platform may require each of them to share a single broadband antenna.
Any of the IRA applications described above may, at times, require a portable version of the IRA to enable practical system development. This will occur if a system requires both high gain and portability. High gain forces one to use a large antenna, while portability suggests a small design. IRAs are generally fabricated from a solid reflector, which is clumsy to deploy and transport particularly when it reaches a certain size.
Several issued patents address the need for portable antennas and describe various collapsible configurations, some of which allow for stowing and deploying a paraboloidal reflector. None of these patents include the features of a broadband feed enabling a broad bandwidth for the antenna, collapsibility, and portability. U.S. Pat. No. 3,707,720 entitled, xe2x80x9cErectable Space Antennaxe2x80x9d to Staehlin et al. describes a collapsible antenna for use in space. The antenna described is not applicable for a large bandwidth or for ultra-wide band use; the reflector is flat and cannot achieve a paraboloidal shape thereby compromising the available gain.
U.S. Pat. No. 4,642,652 to Herbig et al., entitled, xe2x80x9cUnfoldable Antenna Reflectorxe2x80x9d discloses a collapsible antenna wherein bracing wires placed behind the antenna are used to provide the tension force to maintain the antenna""s shape. U.S. Pat. No. 5,963,182 to Bassily entitled, xe2x80x9cEdge-Supported Umbrella Reflector with Low Stowage Profilexe2x80x9d discloses an umbrella-type antenna for use on a spacecraft where the ribs of the antenna are fixed in a parabolic shape using a rigid truss structure. U.S. Pat. No. 5,635,946 to Francis entitled, xe2x80x9cStowable, Deployable, Retractable Antennaxe2x80x9d discloses a retractable and deployable antenna wherein cables are used to deploy as well as support the reflector. U.S. Pat. No. 4,899,167 to Westphal entitled, xe2x80x9cCollapsible Antennaxe2x80x9d discloses a collapsible antenna where rigid saw-tooth shaped segments collapse into one another to collapse the reflector. U.S. Pat. No. 3,618,111 to Vaughan entitled, xe2x80x9cExpandable Truss Paraboloidal Antennaxe2x80x9d discloses a collapsible antenna made up of a plurality of interconnecting hinged solid triangular supports making up a truss antenna structure. U.S. Pat. No. 3,982,248 to Archer entitled, xe2x80x9cCompliant Mesh Structure for Collapsible Reflectorxe2x80x9d discloses a collapsible antenna made of a wire mesh structure with spring-loaded wires that expand to a certain shape when deployed. The elasticity of the mesh allows the material to take shape when deployed. U.S. Pat. No. 4,295,143 to Winegard et al. entitled, xe2x80x9cLow Wind Load Modified Parabolic Antennaxe2x80x9d discloses a collapsible reflector boom having two parabolic reflectors mounted thereon. Solid reflector elements make up the two symmetrical parabolic reflectors.
None of the antennas described in the above patents provide a lightweight, portable, ultra-wideband collapsible antenna. The present invention for a collapsible impulse radiating antenna overcomes the deficiencies in the prior art patents by providing a high gain, ultra-wideband antenna that comprises a reflector made of a conductive mesh fabric that is lightweight and collapsible in an easy umbrella-like fashion. The present invention enables all of the applications discussed above and many others, because it is more portable and lightweight than conventional IRAs. In the preferred embodiment, the present invention for a collapsible IRA (xe2x80x9cCIRAxe2x80x9d) weighs only five pounds and is about the size of a typical umbrella, making it easily transportable by an individual, and easily deployable in the field.
In a second embodiment, the CIRA includes expandable seams between adjacent panels of the reflector, enabling the reflector surface curvature to be adjusted from a more focused to a less focused mode. The flexibility of this embodiment provides a collapsible multifunction IRA (xe2x80x9cCMIRAxe2x80x9d).
The present invention is a broadband collapsible impulse radiating antenna having a reflector and feed arms made from a flexible conductive material. The antenna is operational over a broad bandwidth, in a range from below 50 MHz to above 8 GHz. When driven by a step function, the antenna can radiate an impulse on boresight having a full-width-half-maximum of less than one-fifth the time required for light to travel a distance of one reflector diameter in free space. An umbrella-like support mechanism is used to collapse and deploy the reflector. The umbrella-like mechanism consists of a plurality of support ribs, a center support rod, center push rods, feed arm support rods, and a push sleeve. The support ribs are attached to the reflector and are pivotally connected to a central hub and pivot radially inward and outward upon collapsing and deploying the antenna. A push sleeve slides along the center support rod causing the radial center push rods, that pivot at the push sleeve as well as at the reflector, to provide a radial force to the reflector and thereby deploy and collapse the antenna. A center can maintains the center support rod in a fixed position and contains an RF splitter that splits the input signal into two feed cables of equal length leading to the feed point. Expandable seams are optionally provided in the reflector and feed arms so that the surface curvature of the reflector can be adjusted. The antenna is lightweight, weighing less than three pounds per foot of reflector diameter.
A primary object of the present invention is to provide a collapsible broadband IRA antenna that is easily deployed in the field.
A primary advantage of the present invention is that it is compact, lightweight, and can be easily transported and deployed in the field by a single individual.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.